Among other properties, the antennas of portable handsets such as portable phones, portable digital assistance (PDA) and wireless notebook computers, are required to be of small size, efficient, omnidirectional, and installed inside the mobile phone which contains a PCB (printed circuit board) acting as a ground plane.
Monopole antennas installed vertically to a ground plane provide an antenna whose characteristics in terms of radiation pattern; input impedance, etc., are well suited for cellular and other mobile handsets. Consequently, this antenna has been widely used in portable phones, portable radios, cellular phones and personal communication systems. Modern portable phones and especially cellular phone handsets are size limited and use internal antennas. Hence, despite its advantages, the monopole antenna cannot be implemented in modern handsets.
A widely used antenna in modern portable handsets is PIFA (planar inverted F-antenna) which is compact and is mounted above the PCB of the phone handset, where the PCB acts as a ground plane. PIFA suffers from limitations such as a relatively large size including antenna height above the PCB, a relatively high radiation level in the undesired vertical direction, and strong influence of the user's hand and head.
Another solution is the recently proposed MB-1 antenna which is an internal antenna, implemented in parallel to the ground plane (PCB). This antenna consists of a ground plane, a straight line conductor (a “pole”) and a phase shifting element, such as a delay line, used for phase shifting. The MB-1 antenna's characteristics are similar to those of conventional monopole antennas. However, this antenna requires a radiating element that is realized either as a wire held in parallel to the device's PCB or printed on a bare portion of the PCB.